1. Field of the Invention
The invention relates to a washing machine, more particularly to a washing machine that is adapted to be supplied with different levels of water during a washing operation.
2. Description of the Related Art
Referring to FIGS. 1, 2 and 3, in a conventional washing machine 1, a washing operation (T) consists of first, second and third washing cycles. Each of the washing cycles includes a rinsing operation, a draining operation and a spinning operation. The conventional washing machine 1 includes a washing drum 11, a water level sensor 13 that is operable so as to set a desired water level inside the washing drum 11, and a water pipe 111 connected to the water level sensor 13 and the washing drum 11 to enable the water level sensor 13 to detect the water level inside the washing drum 11. When the washing operation (T) is initiated, a control unit 16 activates the water level sensor 13 and a water supply valve 14 to enable water flow into the washing drum 11. Upon detection by the water level sensor 13 that the water level inside the washing drum 11 has reached the desired water level, the water level sensor 13 generates a control signal that is received by the control unit 16. At this time, the control unit 16 deactivates the water supply valve 14 to cut-off the water flow into the washing drum 11, and activates a motor apparatus 17 for continuing with the rinsing operation of the first washing cycle. At the end of the rinsing operation, the control unit 16 activates a water drain valve 15 to drain the water inside the washing drum 11 during the draining operation. The spinning operation is started immediately after the draining operation. The above steps are repeated for the second washing cycle, which follows the first washing cycle, and the third washing cycle, which follows the second washing cycle.
In the conventional washing machine 1, only one water level sensor 13 is used to control the water level inside the washing drum 11 during the rinsing operation of each of the washing cycles. As such, the water level inside the washing drum 11 is uniform during the rinsing operation of the first, second and third washing cycles of the washing operation (T).
The aforesaid arrangement of the conventional washing machine 1, however, results in the following drawbacks: During the rinsing operation of the first washing cycle, a smaller amount of water is required so as to ensure an adequate detergent concentration and agitating force for effective removal of dirt from clothes. During the rinsing operation of the second and third washing cycles, a larger amount of water is required so as to minimize the presence of detergent residue on the clothes. In other words, the presence of a relatively large amount of water inside the washing drum during the rinsing operation of the first washing cycle results in waste of water resources and ineffective washing of the clothes. On the other hand, the presence of a relatively small amount of water inside the washing drum during the rinsing operations of the second and third washing cycles will result in a large amount of detergent residue on the clothes. It is thus desirable to provide a washing machine that is adapted to be supplied with different levels of water during the different washing cycles of a washing operation to conserve water while ensuring effective washing of clothes and the presence of minimal detergent residue on the clothes.
While it is possible to operate the water level sensor of the conventional washing machine so as to set different water levels during the rinsing operation of the different washing cycles, this requires manual supervision of the conventional washing machine during the washing operation.
Therefore, the object of the present invention is to provide a washing machine that is adapted to be supplied with different levels of water during a washing operation and that dispenses with the need for manual supervision during the washing operation.
According to the present invention, a washing machine comprises: a washing drum; water supply valve means for supplying water to the washing drum when activated, and for cutting off supply of the water to the washing drum when deactivated; a first water level sensor operable so as to set a first desired water level inside the washing drum and so as to generate a first control signal when the water inside the washing drum reaches the first desired water level; a second water level sensor operable so as to set a second desired water level inside the washing drum and so as to generate a second control signal when the water inside the washing drum reaches the second desired water level; and a control unit connected to the water supply valve means and the first and second water level sensors. The control unit activates the water supply valve means at the start of first and second washing cycles of a washing operation. The control unit deactivates the water supply valve means upon receiving the first control signal from the first water level sensor during the first washing cycle, and upon receiving the second control signal from the second water level sensor during the second washing cycle.
In the preferred embodiment, the control unit further activates the water supply valve means at the start of a third washing cycle of the washing operation, and further deactivates the water supply valve means upon receiving the second control signal from the second water level sensor during the third washing cycle.
Preferably, the second desired water level is higher than the first desired water level.
The washing machine of this invention permits conservation of water while ensuring effective washing of clothes and the presence of minimal detergent residue on the clothes.